


Chasing that Night

by AkiDreams



Category: Assassination Classroom, 終わりのセラフ | Owari no Seraph | Seraph of the End
Genre: Assassins & Teachers, GoD Past Arc AU, GoD!Guren, I have no talent in title-writing TTnTT, M/M, Shinya trolling :D, Spoilers for Chapter 134 onwards, This spawned from a rampaging plot bunny
Language: English
Status: In-Progress
Published: 2016-04-18
Updated: 2016-05-28
Packaged: 2018-06-02 23:44:51
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 3,445
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6588061
Author URL: https://archiveofourown.org/users/AkiDreams/pseuds/AkiDreams
Summary: <blockquote class="userstuff">
              <p>When someone reaches the peak of the world, there is no place to go but down. Luckily (or not), for the world-famous assassin, there is a silver light waiting to greet him at the bottom and make his existence just a little bit brighter....as long as he doesn't get annoyed to death first.</p><p>Alternatively, an Assassination Classroom AU that nobody asked for.</p>
            </blockquote>





	1. Prologue Time

**Author's Note:**

> "A young boy carelessly passing his days running amok with all the confidence and hope of the world. Running off too far, he finds himself lost in the dark with no one left around."

Shiba Tatsuya.

Esdeath.

Akashi Seijuurou.

Accelerator.

Aizen Sousuke.

Sakamaki Izayoi.

Sora & Shiro of [blank].

There are many people in the world who are considered geniuses in their fields. To be universally acknowledged as a member of this elite class of beings, they must have certain qualities that draws in other people.

A charismatic personality.

A unrivaled history of accomplishments.

Overwhelming prodigious talent.

A remarkable title.

A legend (not) beginning in the 12th century.

An aura of mystery and fantasy.

An infamous reputation. 

One of these chosen individuals is someone that people only ever dare to mention in hushed whispers, one name stands out above the rest as the greatest assassin to appear in the underground world for decades. It has been said that even the world's best security systems cannot stop him from reaching his targets. He uses methods of assassination so cruel and sadistic that his victims would rather kill themselves to avoid the torture. This man can also become anyone in the world at any time or place, with none the wiser.

He is the person that everyone has heard of.

Yet there is no one still in the world today who knows his true identity and appearance.

Nonetheless, his rumours and tales are still spread to every corner of the world.

The name that everyone calls this god of death and destruction as mysterious and unreachable as the night sky.

_The Moon Demon._

* * *

  
_  
_ The calmness of the night was abruptly shattered by the piercing sound of an alarm and rumbling of countless iron gates closing.

Within moments, all lights in the large castle flickered on. Everyone mobilized to find out what had triggered the security system in the home of the most influential man of this region. Was it a thief? A spy? A false alarm?

"Status report!"

"Dining room, all clear!"

"Ballroom, all clear!"

"All exits secured, sir! No one can escape the castle now!"

"OK! Keep searching! I want to see the intruder's cold, dead body in front on me now!"

"Yes sir!"

Securities guards armed with every type of weapon imaginable rushed down the many halls of the castle. They were determined to find out what was going on and eliminate all the threats.

 

* * *

 

A large, ornate door at the end of a hallway was partially opened.

Two security guards hurried across the red carpeted floor to the large room. Quietly pushing the door open, they peered inside cautiously.

The room was deathly silent, without sounds or movements. Only the silky white curtains waved lazily in the night breeze. The decorations in the room were very luxurious. Hand-carved wooden dressers, tables and chairs. In the very middle of the large room, a large, fluffy bed with intricately carved pillars.

The master of the mansion slept peacefully within the soft cavern of expensive white and crimson-coloured pillows and sheets. He was the most influential politican in this area, loved and hated by many. Slowly, the security guards approached the bed.

"Excuse us, master. There are intruders in the premises. We are working to eliminate the threat. Are you ok?"

No answer.

"Sorry to disturb you then, master."

The guard who spoke to the one on the bed bowed and turned to leave. His partner, who was standing quietly at the side the entire time suddenly dashed forward and reached for the covers.

"Hey! Stop!" The first guard yelled out, but it was too late.

With the sheets uncovered, both guards saw the prone form of the man lying on the bed. His face was serene while he slept. Looking down, however, the guard yelped in surprise. The master's velvet nightshirt blossomed with bright red. A katana pierced straight through his chest, also stained red with freshly shed blood.

"T-THE MASTER IS DEAD!!!"

 

* * *

 

While the castle was filled with panic and chaos, one guard muttering quietly to himself walked calmly down the stairs leading to the basement. In a place where everyone was running around and screaming at the sudden news that intruders had murdered the master of the castle in cold blood, no one paid any attention to that one lone individual walking along the halls inconspicuously.

"This job was too boring." The man mumbled quietly. "I'm totally gonna fall asleep right here and now."

A light giggle was heard from the earpiece he wore.

"You're so silly, Guren." The soft voice replied. "Aren't you the legendary Moon Demon? Of course a small job like this would be child's play for you!"

"...Now even you are making fun of me." The man named Guren sighed exasperatedly as he continued to navigate through the castle. "What is with this whole Moon Demon thing anyway?"

"Every famous hero or villain needs a title that people in the world will remember them by." The voice continued on. "Oh, Guren. You should turn right on the next corner and head down the pipes."

"Got it. But couldn't they have come up with something better?" Guren complained while lithely climbing down the hatch and into the pipes without anyone else noticing.

 

* * *

 

"There is an exit up ahead that leads directly across the river." The voice said through the earpiece. "You can get out unnoticed since there are no cameras or sensors."

"You are efficient as always." Guren replied. "I guess I'll be seeing you very soon then. We can celebrate afterwards over dinner."

"Are you asking me out for a date at a time like this?" The voice sounded quite amused.

"No time like the present."

"Heehee, you're so funny."

Guren continued to navigate the tunnels when he noticed a light breeze and dim lights in the distance. He ran forward, only to be blocked by a metal gate that separated him from the outside world. Immediately, he began to speak to his partner on the other side.

"There are metal bars blocking this exit, how long will it take for you to open it?"

"I can do such a simple thing in a minute."

"Of course you can." Guren leaned back against the wall of the dark tunnel as he waited for the gate to open up. Only the darkness of the tunnel and the dripping sounds of water accompanied him.

"How are you doing with the lock?"

"..."

Suddenly, loud footsteps echoed from the other side of the tunnel. It was too dark to see clearly, but Guren could sense a large number of people approaching. From the heaviness of their steps, they appeared to be heavily armed and clad with military suits. When the footsteps ended, a deep voice emanated from the group.

"The infamous Moon Demon, was it? Pleasure to meet you." The man's voice was harsh and condescending. "I have been wanting to talk to you for quite a time."

"Unfortunately the feeling isn't mutual." Guren snarkily replied. "So if you and your lackies back there could kindly get lost, I have a dinner date to get to."

_Isn't the gate unlocked yet? What's taking so long?!_ Guren thought impatiently. 

"Too bad for you, that gate will not open anytime soon." The man smirked as he walked closer. Under the dim light coming through the metal bars of the gate, Guren could make out the form of an arrogant man with dark hair and strangely jagged eyebrows. "In fact, you won't be getting through to that partner of yours for help either."

"What do you mean?!" Guren turned away to talk into his earpiece. "Hey! Are you there? Answer me!"

"Moon Demon, you're coming with me whether you like it or not." The man stated flatly. Behind him, all the others raised their weapons at Guren.

"What's going on, _Mahiru_!?! _"_ Guren yelled out amongst the sound of gunfire. A shot struck Guren in the side with piercing pain. Slowly, a feeling of numbness began to spread throughout his body as he was sapped of his strength. As he fell towards the ground, a soft, almost inaudible voice drifted from his earpiece.

"Sorry, Guren. This is goodbye."

His vision gradually blacked as he faded into nothingness with only one thought swimming in his mind.

_Mahiru......Why?_


	2. Guinea Pig Time

**Summary for the Chapter:**

> "No matter how much he ran, the young boy could not escape the dark world he found himself stuck in. Looking up, he longed to see the sun once again, but only found the moon staring down at him."

Guren woke up with a groan and a mind-splitting headache. Even without opening his eyes, he could tell that he was in an unfamiliar location.

Heat from bright lights beat down on his skin. The dull whirring of machinery in the background worsened his migraine. Cold, metal bindings restricted his limbs from moving.

Guren remained motionless as he recalled his memories and tried to grasp the situation he found himself in.

"I see that you are awake."

A voice from a nearby speaker boomed. Even then Guren did not make the slightest twitch as he continued to think back to how he ended up in this suspicious place.

"There's no point in pretending to sleep. I can tell by your heart monitor that you are conscious right now."

"Tch."

Guren opened his eyes, only to find himself in an isolated room. The entire room was white, from the walls and floor to the hard surface and lab rat clothes that he found himself in. Everything around him was made of cold metal, giving the space a lifeless and ominous aura. Only one wall was different from the rest, being transparent in colour. It appeared to be made of thick glass. On the other side, there was a sealed metal door and a desk with a computer on it. Guren felt as if he was a zoo animal put on display within an exhibit, the only difference being that he had no audience at the moment.

"I hope you appreciate the housing arrangements we prepared for you." The voice began again. It appeared to be coming from a speaker in the corner of the ceiling. "This is a state-of-the-art research facility built just for you. We are expecting a lot from this experiment so try not to be a disappointment."

"Like I give a crap about you and your experiments." Guren muttered angrily under his breath.

"Us, the Hiiragi clan will revolutionize the world with our research here." The haughty voice continued, disregarding Guren's earlier comments. "Of course, it may interest you more to know that the head researcher working under me is someone you are very familiar with."

"What nonsense are you spouting?!"

"Hmm...no need for denial." The voice responded. "Surely you remember your favourite little partner, Hiiragi Mahiru."

"!!!"

"She has been working with me to plan this project for a long time."

"T-that's a lie!"

"In fact, the one who suggested to use you as the perfect specimen for this experiment was her."

"LIKE I'D BELIEVE THAT!!!" Guren yelled loudly, struggling againsts his binds. "LET ME SEE MAHIRU!! CALL HER HERE YOU LITTLE --"

"I am the noble Hiiragi Kureto, the commander of this place." The voice announced. "Someone elite like me does not have to listen to the ridiculous requests of a lowly mongrel like you."

With that, the speaker crackled and the line of communication ended. Guren, now left alone, began to thrash around and shout loudly although his restraints prevented him from moving much.

 

* * *

 

"Good morning." The speaker crackled to life and Kureto's voice sounded from it. "I hope you had a restful night. Today will be very busy, you see."

"...."

On cue, a team of scientists in white lab coats and masks entered the room Guren was currently held in with various machines and tools. They began to hook him up to various machines and monitors.

"Begin today's tests." Kureto ordered.

For the next few hours, Guren was subjected to all sorts of experiments. From being injected with suspicious substances and shocked with electromagnetic pulses, scientists tried every method at their disposal to achieve their goal for the day.

After growing up in the streets all his life, desperately fighting to live in a survival-of-the-fittest world, Guren was no stranger to pain and hardship. Over the years, he had learnt to trust only himself and his abilities as an assassin. In order for him to acquire those skills, he had struggled greatly and had been beaten down many times by those in power. In the end, he sharpened his blades and his wits in order to strike down everyone in his way.

Compared to all his struggles in the past, something like being experimented on was nothing special.

_In fact, this place doesn't even seem that difficult to get out of._ Guren thought smugly as he smirked.

_I could probably blow up this garbage dump and everyone in it on the way out._

_But their experiments seem interesting, so I'll let them help me get even stronger._

_After that, I'll wait for the right opportunity and get away from here with Mahiru!_

* * *

 

The experiments lasted most of the day. By the time the scientists carted the equipment away, both the experiment team and Guren felt exhausted. His arms and legs ached as if he had fought through squadrons of elite soldiers with only a set of cutlery at his disposal.

Much to his chagrin, the speakers crackled once again as he was resting on his 'bed', signalling that a certain someone was about to speak to him.

"Good work." Kureto's mocking tone bounced off the walls of the small, white room. "As expected of a world-famous assassin, your endurance is praise-worthy."

Finding it too tiresome to even retort with a snarky remark, Guren just laid there and acted as if Kureto did not exist.

"Hmph." Kureto did not seem to take being ignored very well. The sealed door on the other side of the thick glass opened to reveal Hiiragi Kureto in the flesh. Guren looked across the room with an uninterested gaze as Kureto walked up to the glass and continued his speech.

"Everyday, you will undergo similar experiments. After that, for the sake of maintaining your physical well-being as a test subject, you will be given a hour of rest. Then, you shall be questioned and monitored in regards to your condition and progress. Do you understand?"

"So I'm going to have you see you and your horrendous eyebrows every day as well? That is going to really suck then..."

Kureto appeared to materialize a remote control out of nowhere and pressed a button. At that time, Guren felt painful electrical shocks running through his body and sending him hurtling towards the ground below.

"As much as I would enjoy watching you be tormented, I am far too busy with more important affairs to bother with something as menial as coming in to monitor the likes of you." Kureto looks unfazed by Guren's taunts, but his tone of voice dripped of venom and suppressed annoyance. 

"That's  _really_ unfortunate." Guren managed to groan out.

"So I've assigned someone else to monitor you and your progress."

Right on cue, the door opened once again and a voice drifting in from the outside. Light footsteps echoed from the hallway beyond the doorway. Kureto paid no mind as he continue to watch Guren like a hawk.

"Did you call for me~? Kureto-nii-san~?" The edges of a shadow could be seen at the edge of the doorway, getting larger with each step. Finally, a figure could be seen in the doorway. From afar, Guren could catch the glimpse of silver-white hair and...a _tail_?!  _What?!_

"Your new assignment in to monitor this subject's progress daily." Kureto spoke with a serious and commanding tone. "He is an infamous assassin known around the planet so make sure you don't let him escape or fall for any of his tricks like an imbecile."

"Yes~"

What entered the room was a small tiger cub with silver-white fur streaked with black stripes. It's tail waved lazily in the air behind it as scratched its ears lightly. Kureto continued to speak as if everything was normal while Guren stared at the newcomer with widened eyes.

"I trust that you have memorized the file I gave you about our little test subject here, right?"

"Yup~"

Unable to hold it in any longer, Guren interrupted Kureto's conversation with his 'new monitor' with a question that has been burning inside of him.

"So...my new monitor is a kitten."

Kureto turned around, confused but much too proud to show it on his face. Upon noticing the tiger cub at the door, his eyebrows twitched slightly in irritation.

"What do you think you're doing, Shinya."

"Eheheh~" The person named Shinya giggled softly by the doorway. Noticing it's beloved master, the young tiger cub ran back out towards the person and leaped. "Sorry, nii-san. So where is Mahiru's new plaything again?"

"What did you call me?!" Guren was irritated already, even though he had only know this Shinya person for a few minutes. "Show yourself, you little --"

The one that appeared was a young man with soft, silver hair lightly falling in front of his clear, blue eyes. With the purring tiger cub in his arms, he walked into the white room, standing beside Kureto. He looked like a frail, gentle man that could easily shatter like a porcelain doll when handled roughly, if it wasn't for the mischevous smirk he wore and the devilishly amused look in his eyes. Still, Guren was entranced by the new arrival before he remembered that this man was a snarky brat, and one somehow related to Kureto no less.

"Tch." Guren looked away to the side, wanting nothing more than for these two annoyances to get out and give him some peace right now.

Unfortunately, Kureto had absolutely no intention to given his guinea pig anything but more experientation, taunts and torment. Thus, he spoke once again in his signature haughty tone.

"Shinya, you better complete your job quickly and efficiently. Even someone like you can record data and observations, I hope."

"You can count on me, Kureto-nii-san~!" Shinya said as he turned towards Kureto with a blinding grin and a over-dramatic mock salute. Kureto just stool there, unamused. 

"It would do you well to cooperate obediently and not try anything funny. Otherwise, our state-of-the-art facility here has many ways to make sure you listen that I am more than happy to try out." This line, as well as the glare that came with it, were both directed at Guren.

_I'd like to see you try._ Guren thought. _If I wanted to I could slaughter everyone and leave right now, but doing that won't get me anything._

"I have many important documents and reports to go over," Kureto stated as he walked out of the room. "I expect the two of you to serve me well."

With that, Guren was left alone in the room with a mischevous pretty-boy and his oversized kitten.

When the silence became too heavy, Shinya tried to start up a conversation with a hestitant smile.

"So...How about you tell me a little bit about yourself?"

"Hn." Guren seemed intent on ignoring his entire existence.

"Fine, I'll start." Shinya sighed. "I'm Hiiragi Shinya. I'm a teacher at Nihon Teiki Gakuen. I like cats and jam. Now it's your turn!" 

"My name is none of your business. I am an assassin that will murder you and your entire freakshow family eventually, especially that eyebrow freak you call a brother." Guren grumbled out. "I don't feel like telling you my likes, I can say I extremely dislike you Hiiragis though. Happy?" 

Shinya only chuckled lightly, not appearing the least bit by Guren's harsh words.

"Ahaha~ So mean~! Just one correction you might want to make though..."

"What?"

"Unfortunately, I'm adopted~" Shinya nonchalantly announced. "So I'm more like half a Hiiragi!"

"..." If Guren was surprised by this reveal, he definitely did not show it on his face. "...you still piss me off."

Through the speaker, the ever arrogant voice of Kureto interrupted the pleasant conversation going on in the room.

"Shinya, I want you and the results out here now."

Before he could reply, the communication link already shut off.

"Aww, I guess time's up~! Time sure flies when you're having fun~"

"You and I have very different definitions of fun." 

Shinya laughed softly as he walked towards the door with his clipboard, his loyal tiger cub closely behind his feet. Stepping out into the hallway, he could not resist turning back to throw one last remark towards the dark-haired male sitting in the enclosed room.

"See you tomorrow, Mr. Grumpy~!"

Guren resisted the urge to throw something at the silver-haired man, despite the fact that there would be no way he could succeed with the thick glass wall in the way. Lying back with his eyes closed after a long day, Guren drifted off to sleep thinking about gentle silver lights and ashen purple skies. 

**Notes for the Chapter:**

> Sorry for taking so long!!! Life and internet issues ^.^" ...oh and crying about Assassination Classroom coming to an end TT.TT
> 
> Hope you enjoyed this installment :3   
> There would have been more interactions, but Guren can be very grumpy and uncooperative when he wants to :/
> 
> For those of you that follow the manga of Seraph, hopefully this fic can help make up a little bit for the lack on Shinya there and all the crap he has to go through (*cry*).

**Author's Note:**

> I hope you enjoyed this prologue! Though random extras had more screentime than the main charas here XD I can guarantee that will not happen in the actual chapters!
> 
> I mainly wanted to get this up before the anime ended (or reached GoD arc)...but I can pretty much guarantee that I will not be able to finish this by that time :P It's not going to be a long story (just a handful of chapters) but will maybe become quite spoiler-y from now on (though the cast does take the story and do their own thing with it XD).
> 
> BTW the lists at the beginning were made from various google searches and contributions from friends and whatnot....they may/may not reflect my actual opinion (lol I only properly watched/truly know about 70% of them)
> 
> Hopefully you will be entertained as this journey goes on till the end! :3
> 
> Also the beginning notes will pretty much be telling a random mini-tale or something of their own :P just because~ since I couldn't really think of a good way to do chapter intros for this. XD


End file.
